Nucleophilic addition to olefins. 19. Abnormally high intrinsic barrier in the reaction of piperidine and morpholine with benzylideneacetylacetone

Journal Article · Wed Nov 26 04:00:00 EST 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00284a043· OSTI ID:6953085

Bernasconi, C F; Kanavarioti, A

The title reaction leads to the formation of the zwitterionic Michael adduct T/sup +/-/ (PhCH(R/sub 2/NH/sup +/)C(COCH/sub 3/)/sub 2//sup -/) which is in rapid acid-base equilibrium with its anionic form T/sup -/ (PhCH(R/sub 2/N)C(COCH/sub 3/)/sub 2//sup -/). Rate (K/sub 1/, k/sub -1/) and equilibrium constants (K/sub 1/) for nucleophilic addition and the pK/sub a/ of the T/sup +/-/-adducts were determined in 50% Me/sub 2/SO-50% water at 20/sup 0/C. From an interpolation of the rate constants to K/sub 1/ = 1 an intrinsic rate constant, log k/sub 0/ = 0.3, was determined. This value deviates negatively by approximately 2.5 log units from a correlation of log k/sub 0/ for amine addition to five olefins of the type PhCH=CXY, with log k/sub 0/ for the deprotonation of the corresponding carbon acids CH/sub 2/XY. Two major factors are believed to contribute to this depressed intrinsic rate constant or enhanced intrinsic barrier: (1) steric inhibition of resonance in T/sup +/-/ with the steric effect developing ahead of C-N bond formation (this conclusion is supported by an X-ray crystallographic study of p-methoxybenzylideneacetylacetone which shows that steric hindrance to optimal ..pi..-overlap in the adduct T/sup+/-/ is already present in the substrate); (2) intramolecular hydrogen bonding in T/sup +/-/, which is inferred from abnormally high pK/sub a/ values and whose development lags behind C-N bond formation. These effects are shown to be manifestations of the Principle of Nonperfect Synchronization.

• Research Organization: Univ. of California, Santa Cruz
• OSTI ID: 6953085
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:24; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACETYLACETONE
ADDUCTS
AMINES
AROMATICS
AZINES
CHELATING AGENTS
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
EQUILIBRIUM
ETHERS
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
KETONES
KINETICS
MEDIUM TEMPERATURE
MORPHOLINES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PH VALUE
PIPERIDINES
PYRIDINES
REACTION KINETICS
REAGENTS
THERMODYNAMICS